The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Removing organic vapors from air emission points in industrial facilities has been practiced for many years as a way to recover and recycle valuable chemicals as well as reduce emissions of hazardous air pollutants. Many industries have large volumetric air emission points with low organic vapor concentrations that have proven a challenge to recover and recycle. Synthetic adsorbent media have been developed that are effective in removing organics in dilute concentrations from an air stream. This synthetic adsorbent material, however, is costly, and thus, systems need to be developed to use this adsorbent media in an effective way to capture and recover the organic material as well as regenerate the adsorbent media for reuse.
Typically, fixed bed adsorbers can be employed with the synthetic adsorbent media to capture and recover organic materials. Fixed bed adsorbers, however, can require a high flow rate in order to effectively capture and recover the organic materials. The high flow rate and the resultant pressure drop can require high energy blower systems, which utilize significant amounts of electrical energy. Fixed beds can also require extensive down time between cycles, as hot gas is generally used to remove the contaminant from the adsorbent, which then must be cooled prior to the next adsorb cycle. In order to eliminate the down time, two and sometimes three fixed beds are required depending on regeneration cycle time. In addition, due to their stationary nature, fixed bed adsorber systems typically cannot expose all of the synthetic adsorbent material during the adsorb cycle, which can result in short adsorb cycles and poor utilization of the synthetic adsorption material.
The synthetic adsorption material can also be used with a fluidized adsorber. Fluidized adsorbers can enable the adsorbent media to travel continually through the bed. Generally, in a fluidized adsorber, clean adsorbent media can enter at the top of the adsorber and can cascade through multiple perforated plates where it is fluidized by an emission stream that can enter from a bottom of the adsorber. The adsorbent media can flow through to the bottom of the adsorber, and can be transported to a regeneration system, which can regenerate the synthetic adsorption material and can recover the contaminant for reuse or destruction.
Fluidized adsorbers, however, can require a narrow range of flow rates to maximize adsorption efficiency. In this regard, if the flow rate is too low, then the adsorbent does not fluidize, and the adsorption efficiency is very low. If the flow rate is too high, then the resin can be carried over with the emissions air stream, which can cause loss of the adsorbent material. Generally, maximum adsorption efficiency can be obtained by relatively low fluidization velocities, which can require a large footprint for the fluidized adsorber.
A moving bed adsorber can also be used with a synthetic adsorbent material. Generally, in a moving bed adsorber, the adsorbent material can be passed through an inclined channel that can include louvers on an entrance to the channel. A resin retention screen can be positioned at an outlet of the channel. The moving bed adsorber has allowed for an increase in throughput (linear velocity) of the emissions air stream when compared to fluidized adsorbers, but the adsorbent material handling system employed by moving bed adsorbers can promote attrition of the adsorbent material, and can also require additional capital for the collection of the adsorbent material.
Accordingly, there is a continuing need for a system for removing organics form air emission streams that has excellent removal efficiency, can work over a wide range of volumetric flow rates, has low energy usage and lower capital cost.